The present invention relates generally to a composition for billboard sheeting. More particularly, the invention relates to a composition of a compounded PVC substrate for printable billboard sheeting, wherein said composition has excellent weathering, printability, colorfastness, fungicidal durability, extruder processability, non-flammability and thermal stability, where the processability and thermal stability are sufficient to form a full width billboard sheet that is seamless. The seamless billboard sheet is produced on exceptionally wide converting lines utilizing a full width extruder die.
In the past, roadside printable billboards have been typically plastered with imaged paper and/or canvas sheeting. Today most of the paper and canvas sheeting has been replaced with plastic sheeting that is substantially a polyester scrim coated with a substrate. The substrate is comprised of a compounded PVC. There are substantially three methods used to form the sheeting. A first method is to apply multiple coats of plastisol of PVC onto the scrim. A second method is to laminate two extruded PVC films to an interposed scrim using a plastisol of PVC. A third method is to extrude, onto the scrim, a PVC composition. The latter method is preferred over applying plastisols because, generally, it is easier to print on extruded PVC than on a film formed from a PVC plastisol. The reader is reminded that a PVC plastisol is substantially a plasticizer into which is dispersed PVC. Many additives may be incorporated into the dispersion to stabilize the plastisol. In the first method, after coating the plastisol onto the scrim, the coating is heated to a temperature where the PVC and the plasticizer become miscible, whereupon the system inverts and the PVC absorbs the plasticizer. A drawback to PVC plastisols is that the additives in plastisol formulations can interfere with the printing process. The plasticizer and the additives can affect the surface tension and form a thin layer where there is poor adhesion. Another source of compounds that can interfere with printing originate from the PVC polymer. PVC plastisol formulations are compounded with emulsion PVC resins. Residual emulsifiers (soaps) from the emulsion polymerization are by design not soluble in the PVC, and their presence on the surface of the sheet can negatively impact the wetting characteristics. Plasticizers and additives tend to migrate through filmic PVC, so that even billboard sheeting prepared using the second method has similar printing issues, as the plasticizers and additives migrate to the surface. Furthermore, if the extruded PVC of the second method is compounded with lubricants that are subject to plating out, (i.e. polyethylene waxes, metallic soaps and amide waxes), the surface of the PVC film has poor printability. A major advantage of plastisols is that they can be used to coat very wide webs. Wide webs are desired because full billboard width will be seamless. Also, wide webs are desired because they can be cut down to narrower web widths, therein reducing the number of SKUs in the manufacturing queue. Narrower webs must be spliced together to form fill billboard width sheeting, and the splices or seams are thicker than a single ply sheeting. Another problem with narrow sheets is that they are xe2x80x9cheat seamedxe2x80x9d, using radio frequency (RF) welding, and RF welding creates a seam having potentially poor printability. Printability is affected by localized heating, which drives the additives to the surface. Poor printability causes visual distortions of the image.
As previously stated, sheeting produced using an extruded coating of compounded PVC generally has superior printing characteristics. A complicating factor is that PVC compositions are relatively thermally unstable at temperatures required for the extrusion. Uncompounded PVC starts degrading at 120xc2x0 C., forming HCl gas, and the degradation is accompanied by yellowing, and losses in mechanical and rheological characteristics. Typical extrusion die temperatures are about 180xc2x0 C. Thermal degradation is exacerbated with wide dies. With wide dies, the dwell time in the die lengthens, and therefore there is more time for thermal degradation. Heretofore, there has not existed a PVC composition having adequate thermal stability for exceptionally wide dies, and only narrow web extruded PVC billboard sheeting could be formed, which would then be seamed together.
A partial explanation for the difficulty in compounding a PVC composition for billboards is that in addition to having improved thermal stability, it must also have good weathering, colorfastness, fungicidal durability and be flame resistant (e.g. meet NFPA 701 vertical burn). The inclusion of additives to affect these properties has the cumulative effect of making the extrusion process even more complex and thermally challenging. For instance, in order to make the PVC composition flame resistant requires the inclusion of flame retardants, and in general, flame retardants exacerbate thermal degradation during extrusion. The PVC composition must also be compounded to be resistant to light aging, and particularly to UV light. Both flame retardants and UV stabilizers are known to cause embrittlement and yellowing during extrusion, which is unacceptable for billboard sheeting. Antimicrobials, and particularly fungicides are added to affect fungicidal durability. Biocidal agents are sensitive to heat, and loose their efficacy when exposed to high temperatures. Opacity and whitening additives are required to achieve billboard sheeting having sufficient whiteness, opacity and ink receptivity. Typically, these additives are pigments (i.e. titanium dioxide), and they like the previously enumerated flame retardants (i.e. antimony oxide) are usually powders, and their inclusion in the composition, when added to the extruder barrel can significantly increase the friction. A rule of thumb estimate is that 80% of the heat generated in an extruder is the result of the mechanical work input into shearing and mixing the polymer. The addition of powders results in higher friction and more heat being generated. Currently, the widest billboards are approximately 18 feet ( greater than 5 meters), and so an extruder having a die length of 215 inches (5,486 mm) would be required for full width seamless sheeting.
What is needed is a composition of a compounded PVC substrate that has sufficient thermal stability and printability that a full billboard width web can be produced.
What is needed is a composition where the addition of powders, particularly inorganic powders such as antimony oxide, titanium oxide and calcium carbonate, does not result in overheating in the extruder or die.
An economic consideration is the cost of the compounded PVC substrate for printable billboard sheeting. The previously discussed additives are expensive, and a component offsetting their cost is desired. The component cannot increase friction heat, nor negatively impact other processing criteria. The component cannot cause yellowing, nor reduce flame resistance, nor resistance to weathering, nor lower fungicidal durability, nor printability, and yet still lower cost.
The reader is reminded that billboard sheeting is printed using digital printing technology and ink jet printers. Ink jet printing equipment is manufactured by a number of manufactures including Sitech, Vutech, Nur and others. Current ink jet printing equipment is capable of producing indoor as well as outdoor digitally imaged printable billboard signs over five meters (5 m) in width and having at least four (4) aesthetically pleasing colors (yellow, red, blue and black).
Pigment based inks for use in producing indoor and outdoor digitally imaged printable billboards are manufactured by a number of manufactures, including A. R. Monteith, Triangle, Inkware, Akzo, Ink Design, Nur and others. A number of solvents typically used for maintaining the various pigments in solution include: lactic acid, propionic acid, methyl ethyl ketone (MEK), cyclohexanone, 4-hydroxy4-methyl-2-pentanone, methyl-2-pyrrolidone, butyl ester, 2-hydroxy ethyl ester, ethylene glycol monobutyl ether, propylene glycol mono methyl ether, acetate, ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol methyl ether acetate, butyl benzyl phthalate, ethyl-3-ethoxypropionate and aromatic naphtha.
Morgan et al. in U.S. Pat. No. 4,083,789, teaches a series of PVC compositions that are compounded to reduce smoke and flame emissions. The master formulation contains 100 parts by weight PVC, 55 parts plasticizer, 3 parts epoxidized linseed oil, 2 parts Baxe2x80x94Cd complex (stabilizer), and 12 parts of filler. Various fillers are disclosed. They include calcium carbonate, aluminum trihydrate, magnesium oxide, and kaolin. Various plasticizers are examined. They include brominated, chlorinated, and other halogenated phosphorus esters. A particularly useful composition contained Dawsonite.
Carette et al. in U.S. Pat. No.5,194,470, discloses compositions for stabilizing chlorinated polymers. The PVC compositions utilized a minimum quantity of epoxidized oils. Present were organic zinc compounds, and additionally there were organic calcium, magnesium, barium or mixtures thereof; admixed with the PVC. Not mentioned were Baxe2x80x94Zn compounds, nor Montan wax, nor the utility of using perchlorates, or biocides like 10,10-oxybisphenoxarsine.
J. Michael Wallen in U.S. Pat. No. 5,030,676, discloses a UV light stabilizer PVC composition. The composition has titanium dioxide, which is an excellent UV stabilization system, and manganese oxide. The manganese oxide is less than the titanium and still imports similar color and UV stability.
Erwied et al. in U.S. Pat. No. 4,380,597, discloses a PVC composition stabilized with aliphatic polyhydroxyl compounds containing 4 to 6 OH-groups per 100 parts by weight of polymer. These polyhydroxyl compounds should contain at least one carboxyl and/or carbonyl group and/or double bond. Suitable compounds are gluconic acid, glucuronic acid, ketogluconic acid, ascorbic acid or the alkali metal salts, or alkaline earth salts of the mentioned acids. Other conventional processing additives may be present. The invention is also a process for the manufacture of pipes, profiles, foils, hollow parts by hot forming, with the use of the mentioned additives, and the additional use of paraffin, free fatty acid, epoxidized soybean oil or higher molecular weight ester wax.
In a landmark patent Brecker et al. in U.S. Pat. No. 4,255,320, discloses mixtures of monoalkyltin 2-acyloxyethylmercaptide and/or a dialkyltin 2-acyloxyethylmercaptide in admixture with an alkyltin sulfide to stabilize PVC compositions. Specific sulfides mentioned are n-butyl tin sesquisulfide, n-octyltin sesquisulfide, methyltin sesquisulfide, 2-ethylhexyltin sesquisulfide, isobutyltin sesquisulfide, and n-dodecyltin sesquisulfide.
Summers et al. in U.S. Pat. No. 4,100,325, discloses a weather resistant PVC composite. Weather resistance is improved by admixing PVC with gelled polyacrylates. It is apparent that because acrylate is gelled the PVC and the acrylate would not be miscible. Acrylates are known to have good weather resistance, and functionally act principally to affect UV light absorption.
Harvey et al. in U.S. Pat. No. 5,744,525, discloses PVC compositions having impact modifiers, montanic esters, hydrogenated castor oil, tin compounds, and in some cases zinc oxide, titanium dioxide and flame retardants. Cited examples of flame retardants include antimony trioxide, aluminum hydroxide and zinc stannate. Harvey ""525 achieved the greatest stability when N-phenyl-3-acetylpyrrolidine-2-4-dione was added to the PVC composition. Of particular interest are the heat ageing properties as judged through the yellowness index of the variance permeation and combinations disclosed by Harvey ""525. Vinyl chloride resins are thermally stabilized by incorporating a heterocyclic compound, which when in the radical, A=S, are thiophene derivatives, when A=NR, are pyrrolidone derivatives, and when A=O, are derivatives of polyethyleneoxide-propyleneoxide-ethylenediamine (e.g. Tetroni(copyright) compounds which is a BASF trademark). The disclosure does not teach how the compositions will handle in extruder die, nor does it address the issues of flammability and printability.
Holden in U.S. Pat. No. 4,390,585, teaches the method for forming a durable flexible membrane. The durable flexible membrane has a UV stabilizer, which is 2-hdyroxy4-n-oxtyl-benxophenone, and a fungicide which is 2-n-oxty-4-isothiazoline and a fire retardant, which is antimony oxide. Holden ""585 discloses that the additives are coated as a dispersion in a plasticizer, and then the coating is heated in an oven.
The present invention is a composition which is a compounded PVC substrate, where the compounded PVC substrate is suitable as an extrudate in very wide extrusion dies. The composition is particularly suited for printable billboards. The present invention is also the composition that further comprises a scrim, where said composition comprising a scrim is a very wide printable billboard sheet. The present invention prevents printing defects from occurring due to inconsistencies and non-uniformities in the printing surface of a printable billboards sheeting. The composition is a PVC based formulation, compounded to have excellent thermal stability, good processability, weather resistance, flame resistance, good uniformity, and fungicidal durability. Typically, the dies are in the neighborhood of 215 inches (5,461 mm) wide with an average lip opening of 1.5 to 2.0 mm. The composition does not burn, and has only minimal lubrication additives. The composition is also suitable for narrower width dies, such as 1 inch (25.4 mm), and any intervening width.
The PVC composition is comprised of PVC, preferably a suspension resin of PVC having high porosity. The high porosity improves printability, as ink jet inks are partially absorbed by the resin. A preferred PVC is Oxyvinyl""s PVC homopolymer 240FG.
The PVC resin is plasticized. A combination of plasticizers is generally used. One group of plasticizers is alkyl phthalates, and particularly diisodecyl phthalate (DIDP). Another preferred plasticizer is epoxidized soybean oil, ESO. The composition additionally contains a filler such as clay, silicate, talc and calcium carbonate. A preferred filler is calcium carbonate. The calcium carbonate is relatively porous and acts to improve ink receptivity, and the carbonate is basic and serves as a buffer to absorb HCI that may be formed during extrusion. Billboard sheeting is generally white, and the composition contains a colorant that imparts color to the sheeting. The colorant can be added to the composition in the form of a color concentrate comprising an opacifier, a whitener and a blue toner or as a PVC masterbatch or as individual components. Generally, the color concentrate is comprised substantially of titanium dioxide (TiO2), blue toners and optical brighteners. Color concentrates, in the form of PVC masterbatches, typically are compounded with a carrier PVC and additional stabilizers and additives to prevent degradation and augment compounding. Titanium dioxide imparts UV stability, as well as opacity and whiteness. Applicant recognizes that other pigments, such as barium oxide, and other whitening pigments can be used in combination with titanium dioxide or in substitution thereof. A preferred optical brightener is Uvitex(copyright)OB (2,5-thiophenedyl-bis(5-tert-butyl-1,3-benzoxazole) made by Ciba Specialty Chemicals. The composition also contains a flame retardant. Examples of suitable flame-retardants include antimony trioxide and brominated compounds. The preferred flame retardant is antimony trioxide. The PVC, plasticizer, filler, color concentrate and flame retardant account for about 95% of the composition of the formula. The remaining components are comprised of: a.) biocides, and more particularly fungicides such as 10,10-Oxybisphenoxarsine; b.) rheological processing aides, which are substantially polymeric acrylates, such as Rohm and Haas Paraloid(copyright) K-120N, K-120ND, and K-175; c.) vinyl stabilizers, which are predominately barium-zinc stabilizers, such as Witco Chemicals Mark(copyright) 4824,4848 and 4845; d.) lubrication processing aids, and particularly Licowax(copyright) OP powder, a registered product of Clariant GmbH, which is the ester of montanic acids; e.) generic stabilizers, for instance, a thermal stabilizer such as Irganox(copyright) 1076 (octadecyl 3,5-di-(tert)-butyl-4-hydroxyhydrocinnamate), made by Ciba Specialty Chemicals, and a UV stabilizer such as Ciba Specialty Chemicals Tinuvin(copyright) 622LD (butanedioic acid, dimethylester polymer with 4hydroxy-2,2,6,6-tetramethyl-1-piperdine ethanol); and f.) perchlorate stabilizers, such as Witco Chemicals Mark 6087ACM(copyright).
The composition is compounded off line using low shear mixing, such as Banbury mill or roll mill technology, wherein all the ingredients are combined, thoroughly mixed, slabbed and formed into pellets. The pellets are typically dried under slight vacuum.
The composition can be extruded onto a scrim, where the scrim is formed from yarns selected from the group consisting of: polyesters, nylons, polypropylenes, polyamides, polyimides, polyethylenes, cellulosic materials, glasses, polyacrylics, polycarbonates, polyacetals and ketals, polyurethanes, copolymers and terpolymers, and blends thereof. The resulting composition comprises a compounded PVC substrate and the scrim. The composition is reinforced by the scrim, a the scrim adds dimensional stability, and is a reinforced composition suitable for manufacture of very wide printable billboard sheets.
The principal object of the present invention is to provide a composition that is a PVC based substrate having excellent thermal and printing properties, where the composition can be extruded through very wide extrusion dies with so little degradation that there is substantially no yellowing, reduced biocidal durability, deteriorated mechanical properties, nor lowered weather resistance. An example of an exceptionally wide die is a 215 inches (5,486 mm) long, having an average lip opening of 1.5 to 2 mm.
A second object of the invention is to form a full width billboard sheet by extrusion coating a scrim with at least one coating of the composition.
A third object of the invention is to form a full width billboard sheet that has minimal stress induced curling or puckering, wherein there is minimal drawing during extrusion coating and the sheet is annealed.
A fourth object of the invention is to form a full width billboard sheet that has a smooth uniform surface and thickness.
A fifth object of the present invention is to provide a reinforced composition that is a scrim coated with an extrudable PVC based substrate that is suitable for printing.